So now you have shifted to goal post from "providing a simple runnable binary" (not feasible due to baked in third-party licensing) to "open sourcing the game code, so people can rewrite the game to patch the missing parts".

The few examples you point out as "open source released with stubs" are also usually games that are decades old and cultural landmarks, where there was economic incentive from the right holders (good PR) to release them (e.g. Quake). This isn't tennable for your typical game that has to shut down online services because it's financially unsustainable.